Unmasking Hidden Diseases: A Case of Mistaken Identity in Swedish Wheat Fields

When a wheat field gets sick, farmers and scientists often diagnose the problem by looking at the symptoms -a spot on a leaf, a blemish on the grain head. But a new study reveals that what we see might be misleading. The culprits behind these diseases are more versatile and widespread than previously understood, sometimes hiding in plain sight.

To get a clearer picture of the fungal diseases threatening Sweden’s wheat, a team of scientists from SLU, embarked on a nationwide investigation in collaboration with the Plant Protection Extensions of Swedish Board of Agriculture (Jordbruksverket). They analyzed hundreds of samples of diseased wheat leaves and heads from across the country. Instead of just identifying fungal DNA directly from the plant tissue, they took a more hands-on approach: they carefully isolated the living fungi from the samples and grew nearly a thousand pure cultures in the lab. This created a valuable ‘living library’ of the pathogens currently active in Swedish fields.

The investigation confirmed the presence of the usual suspects known to cause ‘leaf blotch’ and ‘head blight.’ But it also revealed a surprising plot twist. The researchers frequently found two species of Fusarium fungus -notorious for causing disease and toxin contamination in the grain heads -living on the leaves and associated with leaf blotch symptoms.

To confirm these fungi weren't just innocent bystanders, the team conducted experiments. They took the Fusarium they had isolated from leaves and applied it to healthy, detached wheat leaves in the lab. The result was definitive: the leaves developed the tell-tale dead spots and lesions characteristic of leaf blotch disease. This proved that these ‘head blight’ fungi could also be responsible for leaf diseases, a fact often overlooked during visual field inspections.

This discovery is crucial for several reasons. It shows that pathogens can be more versatile than we thought, using different parts of the plant as a hideout or ‘secondary niche.’ This allows them to survive and maintain a presence in the field throughout the growing season. Furthermore, it highlights that a simple visual diagnosis can be wrong, potentially leading to ineffective disease management strategies.

This study, published in the European Journal of Plant Pathology under the direction of Salim Bourras (Department of Plant Biology), underscores the importance of this hands-on approach. Building on these findings, the research is now being advanced at the SLU Plant Clinic, where the unique collection of fungal isolates serves as a vital resource for developing future diagnostics and monitoring tool for crop diseases across Sweden.

Read the full publication in open access

Kaur, H., Vilvert, E., Corrales Gutiérrez, M.Á., Zhan, J., Douchkov, D., Desiderio, F., Vélëz, H. and Bourras, S. (2025) ‘Isolation and characterization of fungi associated with wheat heads and leaf blotch symptoms in Sweden’, European Journal of Plant Pathology. doi:10.1007/s10658-025-03096-z.

Funding from the Swedish Research Council for Sustainable Development

Special thanks to Anders Lindgren, Lina Norrlund, Elizabeth Lövstaf, and Elin Almén (Jordbruksverket), Eula Gems Oreiro, Björn Andersson, Fredric Hedlund, and Ayano Tanaka (SLU)

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